At the press conference unveiling the app on Monday, Boston Mayor Marty Walsh said 23 people were killed in crashes in the city in 2015.

"Distracted drivers is one of the biggest risks that we have today, in large part due to cellphone use," Walsh said. "Boston has a history of aggressive drivers. I don't know if we're really worse or better than other cities, but I know we need to make sure that we bring change."

Brendan Kearney of the pro-pedestrian group WalkBoston says the app won't be a silver bullet, but it's another tool to use in the Vision Zero program.

"If this helps get the word out about Vision Zero and reducing fatalities and serious crashes by being more courteous about how you get around the roads, it's great," Kearney said.

The city says the competition will finish in mid-December when the safest drivers in the region will be recognized based on their performance. The grand prize is $2,000.

To be eligible to participate, users must live in the city of Boston or in the Metro Boston area. To start competing, users download the app from the Android or Apple app stores, enter an email address and ZIP code and then start driving.